This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
Certain abbreviations that may appear in the following text and/or drawing figures are defined as follows:
DDS direct digital synthesizer
TD-DDS time domain direct digital synthesizer
DDPS direct digital period synthesizer (synthesis)
PLL phase-locked loop
DTC digital-to-time converter
SDM sigma-delta modulator
SDDM signal-delta digital modulator
FC frequency converter
LO local oscillator
DM delay modulator
DLL delay locked loop (delay line)
MASH multi-stage noise shaping
Software defined radios and concurrent radios can simultaneously employ multiple independent LO signals. This assumption is also valid for those radio systems that may split a transmission into multiple different frequency bands in a flexible spectrum allocation scheme. Future cognitive radio systems may be examples of such systems.
General reference may be had to FIGS. 1A and 1B, where FIG. 1A shows an exemplary three frequency bands each having a different number of channels (Chx), where certain of the channels are cognitive radio reception channels, and where FIG. 1B shows an exemplary number of channels associated with different radio standards, where certain ones of the channels are multiradio reception channels.
The existing frequency synthesizer approaches known to the inventors are inefficient or even unfeasible to implement in a practical system, when it is desired to create a set of independent LO tones that cover a wide frequency range to facilitate, for example, the implementation of multiple radio standards.
A single PLL-based frequency synthesizer can generate only one independent LO tone at any time. Frequency multipliers, dividers and single sideband mixers may be used to extend the output frequency range and to output several tones. However, the output tones are interdependent since they are generated from the same original source. As a result, in order to generate N independent LO tones N parallel PLL units are required. Unfortunately a set of parallel PLLs requires a large amount of integrated circuit die area (e.g., silicon die area), and as a result will typically not be economically feasible to implement. In addition, practical issues such as interference and coupling problems may emerge, rendering the resultant circuitry unsuitable for use in many important applications.